Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The evolution of protein structures is discussed using cytochrome c, hemoglobin, and neurohypophyseal hormones as examples. Although these substances have different biological functions, their evolution is controlled by the same general rules: their primary structures vary at the level of the species, order, or class, but this variation is restricted by the fact that the biological activity of the protein must not be impaired. Alterations (i.e. substitutions, deletions, or additions of amino acid residues) can therefore occur only in certain positions of the peptide chains, although with different frequencies. The total number of alterations thus represents only the final state of a protein and does not take into account successive substitutions which may have taken place at the affected sites. It can therefore give only a rough indication of the phylogenetic distance between two species. The nature of the substituting residues, on the other hand, is a useful guide to zoological cognateness, since it allows the identification of transition molecules which simultaneously contain amino acid residues from the protein of the protein of the evolutionary ancestor and from the protein of the evolutionary descendant.
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